1. Field of the Invention
The invention concerns an X-ray tube anode, more particularly a rotating anode of the type having a main body made of a light material bearing a target formed by a surface layer of an X-ray emitting material.
2. Description of the Prior Art
In X-ray tubes, notably those used for X-ray diagnosis, the X-radiation is obtained under the effect of an electron bombardment of a layer of a target material, i.e. generally a material, with a high atomic number, that is refractory and is a good conductor of heat such as, for example, tungsten, molybdenum or an alloy containing at least one of these elements. These are the elements most commonly used, but the invention is not restricted to an anode with an emissive material containing these elements or their alloys.
The target layer is bombarded on a small surface, called a focal spot, forming the source of the radiation.
For a long time now, the high instantaneous power values (of the order of 100 KW) used and the small dimensions of the focal spot have led to the use of rotating anodes in order to distribute the heat flux on a greater area than that of the focal spot and to dissipate it more efficiently. This distribution and dissipation of heat is all the more efficient as the linear speed of rotation of the anode is high.
However, this linear speed is limited by the mechanical strength of the anode. Thus, anodes having a metallic base have been proposed to obtain an anode with high mechanical strength. However, this base is heavy, and this is inconvenient when the anode has to rotate at high speed. Thus, with this type of anode, the rotation speed is restricted by this heaviness of the anode. Moreover, at high temperature, there is a risk that the metal will get deformed by warping in a direction perpendicular to its main plane.
To overcome this drawback, it has been proposed to make bodies out of light material such as graphite or carbon-carbon composite material. However, these materials are either excessively brittle or, in the case of carbon-carbon composite material, their homogeneity is insufficient to allow them to be used with high rotation speeds.
Anodes have also been proposed with graphite brazed to the metal part forming the emitting part, but they are heavy.
It is an aim of the invention, notably, to overcome these drawbacks by proposing an anode that has a main body with a particular structure that reinforces the mechanical strength of the anode and is relatively light, enabling use with high rotation speeds.